Bonding method

ABSTRACT

Tank treads, brake linings, rifles stocks, and other devices requiring the bonding of metal to non-adherent materials such as elastomers, non-elastomers, polymers, adhesives and slurried materials, with a layer of metal foam interposed between the metal. and the non-adherent material.

RELATED PATENT APPLICATION

This application is a continuation application of Ser. No. 09/598,181filed Jun. 21, 2000, now U.S. Pat. No. 6,843,876 issued Jan. 18, 2005,which is a continuation application of Ser. No. 09/045,662 filed Mar.20, 1998, now U.S. Pat. No. 6,080,493 issued Jun. 27, 2000.

FIELD OF THE INVENTION

This invention relates to methods of bonding structural materials, suchas metal, to non-adherent materials, such as rubber.

BACKGROUND OF THE INVENTION

Rubber will not directly bond to metal. The metal must first be paintedwith primer prior to bonding the rubber. The primer provides a smallsurface area and low strength bond between the metal and the rubber.Thus, the weak link in the bond is merely the “strength” of the primer.This process is used in products as diverse as car bumpers, armored tanktracks and engine mounts.

For example, armored tank tracks are made of metal machined to form thelinks and track plates which are fitted together to form a continuousbelt. Most tank plates have rubber pads which provide better tractionand prevent the roads from being chewed up by the tank tracks. Inaddition, the “road and bogey wheels” which are found inside the tracksare also generally coated with rubber to increase traction, reduce metalto metal wear, limit vibration in the suspension and reduce the noisethe tank makes in motion.

The steel track plates are painted with primer before the rubber isbonded with heat and pressure. The rubber pad can be separated from thetrack plate by shearing, due to normal operations (acceleration andsteering) or rough road surface, and by heat deterioration, due tofriction and vehicle weight (approximately 130,000 pounds). A completeset of tracks for a U.S. Army M-1 Abrams tank can cost as much as$100,000.00 and may only last from 300 to 2000 miles.

In another example, a car bumper is made of rubber coated steel. Thesteel backing is painted with primer. The rubber is then bonded to theprimed steel with heat and pressure. The rubber coating may stand up tostraight on (perpendicular) forces, but will easily be “peeled” or“sheared” off by forces from the side (lateral forces). This peeling mayeven occur, and thus the car bumper will fail, before either the steelbacking or the rubber has worn.

Aside from the paint-like primer method, other methods have been used toincrease the surface area and strength of the bond between metal andrubber. They fall into three categories: mechanical or chemical etching,machining or channeling, and perforation. Etching consists of abrasive,shot or bead blasting and selective surface erosion by exposure of themetal to acids or strong chemical solutions. Machining or channelinginvolves the use of deeper cuts and bends in the metal. Perforationallows the rubber to penetrate and form plugs which resist delaminationbehind the metal. Each of these methods are expensive, and each methodweakens the metal surface and may concentrate delamination forces withinthe rubber compound, thus defeating their purpose.

In a completely different field, inventors have proposed open-celledfoams made of metal or the like for use as lightweight buildingmaterials, solid propellant reinforcement and burning rate modifiers,battery plates, fluid phase separators, heat shields, heat exchangercores, radiation shields, fluid filters, shock absorbers, as well as innumerous other applications.

Walz, Reticulated Foam Structure, U.S. Pat. No. 3,946,039, Mar. 23,1976, describes the process by which a reticulated foam structure ismade of metals, ceramics, polymers, etc. In Walz' method, an originalpolyurethane foam, or sponge, is manufactured to the desiredspecification of the metal foam which is desired. Then a fluidsuspension of a metallic salt is introduced into the originalpolyurethane foam structure and allowed to set to a rigid structure.This step is called the investment. In this way, a “positive” is formedof the original polyurethane foam structure. The next step is theremoval of the original polyurethane foam structure, so as to provide apattern of voids or internal passageways in the investment whichcorrespond to the original foam structure. In the next step, moltenmetal is poured into the positive which fills the voids of the positive,forming the final reticulated foam structure which is nearly identicalto the original polyurethane foam. Finally, the investment is dissolvedin a convenient medium, leaving a metal foam with all the pores empty.

Under this process, reticulated foams may be prepared of various metals,such as aluminum, steel, beryllium, magnesium, uranium, iron, etc.;alloys, such as aluminum-silicon, aluminum-magnesium, and aluminum-zinc;ceramics-based on aluminum oxide, silicon dioxide, ferric oxide,including refractories, such as carbides and nitrides; and organicpolymers, such as polymides, polyaromatic ethers and thioethers,fluorocarbons. The pore sizes of the inorganic composition vary from 3to 125 pores per linear inch (ppi). Commercially, pore sizes may beobtained in at least a range of 10 ppi to 100 ppi.

Walz, Method of Making an Inorganic Reticulated Foam Structure, U.S.Pat. No. 3,616,841, Nov. 2, 1971, is substantially similar. Others haveimproved on the process, suggesting use of various materials for theoriginal foam, such as natural reticulated materials like sponges andcoral.

SUMMARY OF THE INVENTION

The invention described herein provides a method which increases thesurface area of a metal to rubber bond, dramatically improving thestrength of the bond. Here, a metal foam is attached to the metalstructural element before the molten rubber is cast. The rubber absorbsinto and becomes entangled in the metal foam, forming a superior bondand making it virtually impossible for the rubber to peel off. Theresult is a bond which may have hundreds of times the surface area ascompared with the prior art primer method. This improved bonding methodcan be used for any bond between a structural material, such as metal,and a non-adherent material, such as an elastomer, epoxy or plastic. Themetal foam may replace the prior art use of paint primer, or it may beused in combination with a primer

The uses for this new bonding method are vast. Armored tank tracks madewith this method will save the military millions of dollars each year inrepair costs since the rubber pads on the track plates will last muchlonger. Car bumpers made with this method will be more durable. Brakepads formed by this method will essentially polish brake drums ratherthan gouge them when over-worn. This bonding method may also be appliedto engine mounts, rifle stocks, seals, O-rings, and space applications,such as the heat absorbing ceramic tiles on the space shuttle.

By way of illustration, an armored tank track can be made by taking theexisting track plate made of steel, welding the metal foam to the trackplate, placing the track plate and metal foam combination in the sametrack plate mold used today, pouring liquefied rubber into the trackplate mold and casting under high pressure. The significant differencebetween the prior art and the improved method described herein is theintermediate stage of attaching the metal foam to the track plate priorto priming the track plate before molding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the bonding process described herein.

FIG. 2 illustrates an overview of an armored vehicle track assembly anda breakdown of its components.

FIG. 3 is illustrates the improved method of forming the rubber pad ofan armored vehicle track plate.

FIG. 4 illustrates an improved method of forming automobile bumpers.

FIG. 5 illustrates the current method of forming brake pads.

FIG. 6 illustrates a prior art braking assembly.

FIG. 7 illustrates an improved braking assembly.

FIG. 8 illustrates the current method of forming rifle stocks.

FIG. 9 illustrates the improved method of forming rifle stocks.

FIG. 10 illustrates the improved method of forming engine mounts.

FIG. 11 illustrates the improved method of Teflon coating an O-ring.

FIG. 12 illustrates a heat shield tile.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates the bonding method described herein. A structuralelement 2 is secured to a non-adherent material 3 via the intermediaryfoam 1. Generally, the embodiments and applications of the inventionswill have an intermediary foam 1 made of metal such as aluminum orsteel, a structural element 2 made of aluminum or steel, and anon-adherent material 3 made of rubber or plastic. Here, the structuralmaterial 2 is attached to the foam 1. The part of the foam andstructural material that will be in contact with the non-adherentmaterial are coated with a primer to enhance adhesion such that thenon-adherent material will not peel off of the structural material notcovered by the foam. The non-adherent material 3 in a liquefied form isthen poured over the foam and structural material which has been set ina mold or tooling. The combination of the structural element, foam andnon-adherent material makes up the final composite 4.

The structural material 2 chosen depends upon the user's application.Such materials include any type of metal, ceramic or other material towhich, for example, rubber or plastic is difficult to bond. In a typicalapplication, such as an automobile bumper or armored vehicle track, thestructural material could be steel, chosen for its strength anddurability. In another application, aluminum could be chosen for itspliability and light weight.

The foam 1 used will typically be a reticulated open-celled foam madeaccording to the methods such as those described in Walz, ReticulatedFoam Structure, U.S. Pat. No. 3,946,039, Mar. 23, 1976 and Walz, Methodof Making an Inorganic Reticulated Foam Structure, U.S. Pat. No.3,616,841, Nov. 2, 1971. This foam has a reticulated structure, meaningthat it is constructed so as to form a network of open pores. Other opencelled foams may be used, and closed cell foams and non-reticulatedfoams may also be used.

Open-celled foams can-be made of metals, alloys, ceramics, polymers,etc., and the type selected will depend on the user's application. Poresizes may be obtained in at least a range of 10 ppi to 100 ppi. The moredense the reticulated foam, the greater the surface area of the bond.

Closed-cell reticulated foams could also be adapted for use in thisimproved bonding method. Patten, Closed Cell Metal Foam Method, U.S.Pat. No. 4,099,961, Jun. 11, 1978, describes a method of making aclosed-cell reticulated foam wherein inert gas is trapped within themetal or metal alloy to achieve a porous airy interior, yet leaving thesurface smooth. Closed-cell foams could be adapted for use by, forexample, cutting the foam open and exposing the airy interior. Thesmooth surface could be attached to the structural material, leaving theairy interior exposed to bond with the rubber.

Other “foamed” metals, which could be substituted for the open-celledfoam, have been produced in varying degrees of porosity by a number ofwell documented means. These means include “sintered” metal, plating orbuildup over a foam-like substrate, and rapid cooling off and airinjection into liquid metals. Sintered metal is created by mixingplastic beads with powdered metal, adding a binder, and the mixture isthen compressed and bonded together. The metallic powder is sintered byheating the mixture, with the plastic beads oxidizing, and eventuallyescaping as gas and water vapor.

The foam 1 can be welded to or fastened to (with, for example, nuts andbolts) the structural material 2 prior to coating or molding. Thestructural material 2 can also be cast integrally with the foam duringthe preparation of the foam by placing the structural material at thebottom or other portion of the foam's mold, causing the structuralmaterial to bond to the foam during the foam's cooling, as described inWalz, Reticulated Foam Structure, U.S. Pat. No. 3,946,039 (Mar. 23,1976).

The non-adherent material 3 is chosen depending upon the user'sapplication. Such non-adherent materials include elastomers (rubber,synthetic rubber, urethane), non-elastomers (PVC, polyethylene, etc.),polymers (plastics, nylon, zytel), adhesives (epoxies, resins) or otherliquid, plastic or slurried materials. (brake lining material, ceramics,and other slurries), provided that the non-adherent material in liquidform is capable of becoming a solid in final manufacture, and is capableof penetrating the foam.

Once the structural material 2 and foam 1 are fastened together, thecombined element is then placed in a mold or tooling, ready for molding.The non-adherent material is applied to the structural material withordinary molding processes, which generally require pouring thenon-adherent material into a mold, setting the structural element intothe non-adherent material, and causing the non-adherent material tosolidify on the structural material. Solidification of the non-adherentmaterial may be accomplished by heating, cooling, light exposure,pressure, chemical reaction, dehydration, microwave radiation or othermeans. The non-adherent material travels through the network, becomingentangled within and intermingled with the foam, essentially formingpart of the foam layer. This entanglement makes it nearly impossible forthe non-adherent material to be separated from the foam once thenon-adherent material has solidified. (While pouring is the mostconvenient way to accomplish the molding step, the molding step may alsobe accomplished by applying pressure and heat, singly or in combination,to cause the non-adherent material to intermingle with the foam. Forexample, the non-adherent material may be provided as a powdered polymeror metal, settled into the foam, and melted in place, after which itwill harden to form a layer that is partially or wholly intermingledintermingled with the foam.)

The improved bonding method described herein has vast applications forany elastomeric or plastic molded products. FIG. 2 illustrates theapplication of this bonding method to the track components of thetypical armored tank treads.. The armored vehicle track assembly 5includes track plates 6, rubber pads 7, edge links 8, center links 9 anda connecting rod (not shown). In the prior art, the rubber pad 7 isattached to the track plate 6 using the painted primer method, wherebythe metal track plate 6 is painted with primer and the rubber pad 7bonded to the track plate 6 with heat and pressure. As shown in FIG. 2,each of the track plates is attached to the rubber pads via theintermediate layer of metal foam 10.

FIG. 3 illustrates the improved method of attaching rubber to the trackplate. First, a metal foam 10 is attached to the track plate 6 bywelding the two together, by forming them together, or with fasteners.The metal foam 10 and track plate 6 are then placed into the track platemold 11, (which may be the same mold used in the prior art such that nonew tooling may be required for this molding process). The metal foam 10and track plate 6 are coated with a primer to enhance adhesion to thelattice of the metal foam and prevent the rubber from peeling off theexposed track plate in the areas where the rubber is in direct contactwith the track plate. Rubber is poured into the track plate mold andcast into the desired shape of the rubber pad, then cured to become hardrubber. The areas of black within the foam are rubber, and constituteand integral part of the rubber pad 7 which is intermingled with thelattice of the metal foam, and adheres to the metal foam over a surfacearea that is many times that of the flat area of the underlying trackplate. This results in a much stronger bond that lasts longer and ismuch less susceptible to separation under compressive, tensile and shearforces. A significant difference between the process used today and theimproved method described herein is the attachment of the metal foam 10to the track plate 6 prior to molding, instead of merely painting thetrack plate with primer prior to molding.

The construction illustrated above can be applied in many areas whererubber or plastic must be secured to metal. FIG. 4 illustrates theimproved method of forming automobile bumpers. Here a steel structuralmaterial 12 is attached to a metal foam 13, and the automobile bumpermade of rubber 14 is attached to the metal foam. The casting is executedwhen the molten rubber 14 is poured into the mold 15 over the steelstructural material 12 and metal foam 13. The rubber 14 penetrates themetal foam 13, creating a strong bond when cured.

The new bonding method described herein can also be used in making brakepads. FIG. 5 illustrates the prior art, whereby brake lining material 16(fiber reinforced non-flammable friction materials) in liquid orsemi-solid form is poured into a mold 17 with locator pins 18 for rivetswhich will eventually be installed. The mold is dried until the brakelining material solidifies. The resulting dried pad 19, shown in FIG. 6,is riveted with rivets 20 to the brake backing 21 forming the finalbrake pad assembly 22. One disadvantage of this method is that therivets wear into and eventually destroy the brake rotor or brake drum ifthe pads are worn beyond the depth of the rivets (a common occurrence),requiring that the rotor or drums be turned to recreate a smoothsurface. Also, the rivets tend to break when they contact the drum orrotor, making the brake pad fall off its backing, resulting inuncontrolled braking and extensive damage to the brake system. To avoidthe necessity of turning the rotors and the damage from a thrown brakeshoe, brakes should be replaced when the pad is still thicker than therivets. When drivers actually follow this advice, it leads to waste ofthe friction material.

To solve the problems with riveted brakes, the rivets can be replacedwith metal foam. FIG. 7 illustrates the improved brake pad, wherebymetal foam 23 is welded to the brake backing 21. A hole 24 is thendrilled through the brake backing 21 and metal foam 23 through which topour the brake lining material 16. The mold is dried until the brakelining material solidifies, forming the completed brake pad assembly,here with integrated brake pad backing and no rivets. This constructionprovides a much stronger bond between the brake backing and the frictionmaterial due to the greater area of bonding. It also reinforces thebrake pad structure to prevent fragmenting, and allows use of softermaterials which would cause little or no damage to the rotor or drum andprovide longer life through greater thermal transfer. Also, when thefriction material wears to the metal foam, the rotor is still exposed tosubstantial amounts of brake material to provide braking, and theuniformly distributed metal foam will essentially polish the rotor. Thispolishing may over time cause wear to the rotor, but will not cut deepgrooves in the rotor as done by the rivets currently in use.

Another use for this improved bonding method is for rifle stocks. Riflestocks are constructed of plastics, epoxies, fiberglass, wood orreinforced composites. The gun barrel and action bedding block (whichhouses the rifle action) are molded directly into the gun stock or setinto the stock with epoxy. Gun accessories such as bipods and otherparts are typically fastened to the stock with bolts and bolt receiversmolded into the stock or set into the stock with epoxy. Rifle stocksexperience a variety of stresses, from the actual firing of powerfulcartridges to rough handling in transit or use. Fasteners or bolts usedto hold the gun together frequently pull out of the plastic, epoxy,fiberglass, wood or reinforced composite rifle stocks because of theirsmall bearing surface area. The homogeneous type of bedding block whichis subject to extreme forces, tends to loosen within the stock afterextended use.

An improved method of attaching gun parts together would be to providein the rifle stock a “bed” for a metal foam wherein the action would beembedded. FIG. 8 shows an example of a prior art gun formation where ametal gun barrel 25 and bedding block 26 is attached to the rifle stockcomposite material 27 with one or more bolts 28. FIG. 9 shows theimproved method wherein a welded foam 29 composite made of steel (or thesame metal used for the bedding block) is molded into the rifle stock27. When the rifle stock is molded under the typical molding techniques,the foamed bedding block 29 is set into the mold. Alternatively, metalfoam mounting elements are set into the rifle stock during molding, andthe rifle barrel and action are bolted into the metal bedding blockwelded to foam and set into mold prior to molding. In either case, thepercussive force of firing is borne by the metal foam, and dispersedover a wide area of the rifle stock, thereby avoiding damage to thestock.

The new bonding method described herein can also be used in makingengine mounts. Engine mounts are used to attach, for example, an engineto a car frame, and typically have a high failure rate. FIG. 10illustrates the improved method for making an engine mount 30. Enginemounts typically fail when the rubber ring 31 separates from the metalring 32 which attaches to the vehicle frame or the metal ring 33 whichattaches to the engine block. Separation occurs due the weakness of therubber to metal bond. To alleviate this problem, metal foam rings 34, 35have been interposed between the metal rings 32, 33, and the rubber ring31.

Industrial seals, also known as O-rings, are used in thousands ofapplications, including pipe joints and valve covers to provideair-tight and water-tight seals. The improved bonding method describedherein provides a superior bond where the seals are coated, for instancewith Teflon. FIG. 11 illustrates just one embodiment of thousands ofdifferent metal seals. Here, the metal seal 36 is coated with Teflon 37.As before, a metal foam 38 is interposed between the metal seal 36 andits Teflon coating 37.

Higher temperature foams and ceramics could be combined for spaceapplications. Currently, the exterior of the Space Shuttle is “tiled”with ceramic tiles, which act as insulation against the extremely hightemperatures to which the Shuttle is exposed when the Shuttle enters andleaves the earth's atmosphere. These tiles frequently fall off whenexposed to high temperatures because currently, the tiles are glued onand the glue fails. FIG. 12 illustrates an improved bonding methodwhereby a structural material 39 made of a high temperature metal orother high temperature substance, having an embedded attaching means 40to later be used to attach the final composite to the Shuttle or otherspacecraft wall 41, is attached to a high temperature foam 42. A liquidceramic 43 is then poured over the foam 42 and structural material 39.

In general, the invention is an improved method for bonding a firstmaterial and a second material together, said method comprising securinga foam material to the first material, applying the second material tothe foam material and causing the second material to intermingle withthe foam and then solidify.

Thus, a novel structural material to non-adherent material bondingmethod has been presented. While specific embodiments and application ofthis invention have been shown and described, it would be apparent tothose skilled in the art that many more modifications are possiblewithout departing from the inventive concepts herein. The invention,therefore, is not to be restricted except in the spirit of the appendedclaims.

1. A method for bonding a first material and a second material together,said method comprising the steps of: securing a foam material to thefirst material; and then applying the second material to the foammaterial; wherein the first material is metal, the foam is metal foam,and the second material is selected from a group consisting ofelastomers, non-elastomers, polymers, adhesives and slurried materials.2. A method for bonding a structural material to a non-adherentmaterial, said method comprising the steps of: attaching the structuralmaterial and a foam together; and then pouring the non-adherentmaterial, in liquefied form, over the foam and structural material,wherein the non-adherent material goes through a process ofsolidification; wherein the structural material is metal, the foam ismetal foam, and the non-adherent material is selected from a groupconsisting of elastomers, non-elastomers, polymers, adhesives andslurried materials.
 3. A method for bonding a first material and asecond material together, said method comprising the steps of: providingfoam; attaching the first material to the foam; providing the secondmaterial in liquefied form; and then adding the second material to thefoam; wherein the first material is metal, the foam is metal and thesecond material is selected from a group consisting of elastomers,non-elastomers, polymers, adhesives and slurried materials.
 4. A methodof attaching a non-adherent material to a metal piece, said methodcomprising the steps of: attaching metal foam to the metal piece;placing the metal foam and the metal piece into a mold; and then pouringthe non-adherent material in liquefied form into the mold; and allowingthe non-adherent material to solidify whereby at least a portion of thenon-adherent material intermingles with the metal foam thus securing thenon-adherent material to the metal foam; wherein the non-adherentmaterial is selected from a group consisting of elastomers,non-elastomers, polymers, adhesives and slurried materials.